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000
FXUS63 KTOP 282340
AFDTOP

Area Forecast Discussion
National Weather Service Topeka KS
640 PM CDT Wed Jun 28 2017

...Update to aviation forecast discussion...

.SHORT TERM...(This evening through Thursday)
Issued at 328 PM CDT Wed Jun 28 2017

As of 20z a long wave, mid and upper level trough was positioned
across central and northern CONUS. Water vapor reveals a very subtle
shortwave within the broad trough across CO/WY. At the surface, a
synoptic cold front was oriented from west central KS, northeastward
towards the NE/IA/MN/SD intersection. A substantial field of
agitated Cu was noted on visible along and head of the synoptic
front. Gusty south to southwest surface winds have ushered up rich
Gulf moisture with much of the CWA residing with Td near 70 degrees.
With the veered surface winds, convergence along the boundary is
limited ATM. However, mesoanalysis reveals upwards of 3000-4000 J/KG
of nearly uncapped MLcape along the KS/NE border. Convection has
began to erupt along the boundary in NE and IA. I expect this trend
to continue further south and west into the northern areas of the
CWA. With the large instability and effective shear of 30 to 40kts
in place, expect organized convection with supercellular structures.
Large hail, potentially large than 2 inches in diameter and damaging
wind gusts will be the primary hazards. Given the veered low level
winds, the tornado threat is low. We then transition our focus to
the late evening and overnight hours. Further thunderstorm
development is expected across western KS late this evening as the
modest upper wave ejects into the plains. Upscale growth to an MCS
is expected. The LLJ is expected to be strong once again tonight
with winds approaching 50kts. As it veers through the overnight, the
LLJ and cold pool generation should suffice for MCS maintenance
throughout the overnight. Short term/synoptic and CAM guidance
suggests these thunderstorms will approach north central KS after
midnight, progressing eastward across the area through dawn. Areas
along and north of Interstate 70 appear to have the best potential
for activity. Given the steep mid level lapse rates remaining in
place, MUcape values of 1000-2000 J/KG will continue the threat for
large hail. As the LLJ veers, 0-3KM shear vectors reorientates
towards the line normal of the MCS, therefore damaging winds are
possible as well.

Thursday [29 June 2017]: Overnight convection is expected to exit
the area by mid-morning on Thursday. Remnant OFB are expected to
remain across northeast KS through tomorrow afternoon. Exact exit
timing of morning convection and cloud cover will play a major role
in thunderstorm evolution tomorrow afternoon. That being said,
destabilization is expected by tomorrow afternoon as the main upper
level trough ejects into the central plains. As it approaches the
area, the EML is expected to weaken with isolated to scattered
convection erupting between 21 and 00z tomorrow afternoon/evening. A
deepening surface low/bulging dry line across central KS will help
to back surface winds, hence increase the magnitude of low level
wind shear. Initially, supercell thunderstorms are expected with all
hazards (large hail, potential very large, damaging winds and a
tornado or 2 especially along any OFB) possible. Thunderstorms will
grow upscale into clusters/line segments after 00z. Refer to the
long term discussion for further details.

.LONG TERM...(Thursday night through Wednesday)
Issued at 328 PM CDT Wed Jun 28 2017

By Thursday evening, a surface front will be oriented from the
northwest to the southeast bisecting the CWA.  Almost all models
show ongoing convection in the evening, sans the NAM which builds
ongoing convection in northern Missouri into the area later in the
night.  Any ongoing discrete storms would have the potential to have
very large hail and damaging winds.  Storms are expected to evolve
into (or already be in) a MCS and forward propagate across the area.
 If this were to occur, the main hazard would transition to strong,
damaging winds.  This threat would last into the late night and
early morning before the front moved southeast of the area and any
MCS moves out of northeastern Kansas.  With the potential for rain
tonight along with a possible MCS moving across the area tomorrow
night, flooding will be a concern for Thursday evening.  If the MCS
moves quickly enough across the area then flooding may just be
limited to the local scale.

Friday morning into the afternoon could have a few showers and maybe
a storm mainly near east central Kansas. Northerly winds with the
passing front will limit temperatures to the low to mid 80s.  The
weekend looks relatively dry with the next best chance for storms
not occurring until Sunday night.  Temperatures will be in the upper
80s.  A wave moves across the area Sunday night bringing chances for
thunderstorms through Monday night.  Chances continue through the
4th of July with the GFS and the ECMWF bringing a mid-level trough
over the area.  Temperatures on the 4th of July look to be in the
upper 80s.

&&

.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 640 PM CDT Wed Jun 28 2017

Will maintain VFR forecast. Still enough suggestions of convection
potentially reaching the terminals around 10Z, but restrictions if
any with this would likely be brief. Wind shear remains likely to
develop for much of the first half of this forecast. TSRA chances
increase late in the forecast but too much uncertainty for
inclusion yet.

&&

.TOP WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...Baerg
LONG TERM...Heller
AVIATION...65